This inventions relates to a color image forming apparatus by the photoelectric method, which is miniaturized for improving the maintainability and modified for improving the jamming repairability.
A photoelectric image forming apparatus which forms full color images or monochromatic images comprises a charger for charging a photosensitive drum, image exposure means for exposing an image on the photosensitive drum, a developing unit for developing an electrostatic image on the photosensitive drum with toners, and a transfer device for transferring a toner image from the photosensitive drum to a recording paper which are arranged around the photosensitive drum.
A photoelectric image forming apparatus for full color images comprises three or four developing units, each of which contains a black (BK) toner when yellow (Y), magenta (M), and cyan (C) toners are to be used, and while the photosensitive drum is rotating three times, a black (BK) toner image is formed on the photosensitive drum as well as yellow (Y), magenta (M), and cyan (C) toner images. By transferring the toner images on a recording paper, a full color image is obtained. When such an image forming method is to be used, the color image forming apparatus can be miniaturized by making developing units thinner and arranging three or four of them close to each other.
A color image forming apparatus using such an image forming method is indicated in Japanese Patent Application Laid-Open 55661/1986. The apparatus forms latent images using three laser beams corresponding to the three developing units; and the photosensitive drum, developing units, and cleaning means are integrated to a unit which can be removed from the main unit of the apparatus.
The color image forming apparatus indicated in Japanese Patent Application Laid-Open 55661/1986 is useful for improving the maintainability but has a disadvantage that developers are apt to be dropped or mixed during installation or removal of the unit.
An example of a unitized photosensitive drum and others of a color image forming apparatus for transferring each color toner image on a recording paper using a transfer drum is indicated in Japanese Patent Application Laid-Open 72159/1983, 43170/1988 and 43171/1988.
In the color image forming apparatus indicated in Japanese Patent Application Laid-Open 72159/1983, 43170/1988 and 43171/1988, however:
(1) The image forming section includes not only the photosensitive drum and surroundings but also the transfer drum.
(2) Between the photosensitive drum and the transfer drum, the peripheral speed and the gap must be retained highly accurately.
(3) To remove the photosensitive drum from the main unit, a release mechanism is required.
In a color image forming apparatus using a transfer drum, as mentioned above, the mechanism of the apparatus is complicated and expensive as described in above (2) and (3), and the image forming means are not centralized around the photosensitive drum compared with a monochromatic image forming apparatus requiring no transfer drum, and the image forming section is not provided with a satisfactory advantage of unitization (process unit).
An object of the present invention is to provide a color image forming apparatus which has a cartridge structure that the developing unit, image retainer such as a photosensitive drum, and cleaning means can be inserted or removed as one, or two of them as one and the remaining one independently so as to improve the maintainability, comprises a plurality of developing units which are unitized so as to prevent developers from being dropped outside or introduced into another developing units when some unit, especially the developing unit is to be inserted into or removed from the main unit of the apparatus, and allows easy jamming repair when an error occurs in a recording paper while feeding.
Another object of the present invention is to provide a color image forming apparatus using a process that composite color toner images using a plurality of color toners are formed on the surface of the photosensitive drum and transferred onto a recording paper in a batch, which is structured so that the image forming means such as a plurality of developing units and the cleaning means are centralized around the photosensitive drum to make the apparatus small and compact; and the plural developing units in a flat form are arranged on one side of the peripheral surface of the photosensitive drum. The open direction of the upper frame of the main unit is set so as to provide outstanding operability since the developing unit comprising the plural developing units is heavy.